1. Field
This invention pertains to laser systems and methods which are useful, in particular, for the remote preparation of high density pellets which include a ceramic matrix material and highly radioactive elements.
2. Description of Related Art
High level nuclear fuel waste is generated as a result of the reprocessing of used nuclear fuel from the operation of commercial nuclear power plants throughout the world. In order to dispose of this waste, it is necessary to recover and reduce the long lived highly radioactive elements contained therein. The long lived highly radioactive elements can include Americium (Am), Curium (Cm), Plutonium (Pu), Neptunium (Np), Protactinium (Pa), Californium (Cf), Uranium (U), Thorium (Th), and certain fission products, such as Technetium (Tc)-99, Iodine (I)-129, Zirconium (Zr)-93, Selenium (Se)-79 and Tin (Sn)-126. U can be contaminated with U-232 and/or U-234 and Th can be contaminated with Th-228. Certain isotopes of these nuclear fuel elements have very high and penetrating radiation fields. The radiation fields increase even further when irradiated Th and U are recycled due to the build-up of Th-228, U-232 and associated decay products. In addition, further contamination with radioactive fission products typically formed in a fission reactor may occur. Reducing the radioactivity of the high level waste can be carried out by forming pellets containing oxide, silicide, nitride, or carbide of these highly radioactive elements with a thorium or uranium or zirconium oxide, silicide, nitride or carbide matrix, and then exposing the pellets to an intense neutron spectrum of a nuclear reactor which will ultimately reduce the content of these radioactive elements by transmutation into stable fission products. The high and penetrating radiation fields of the highly radioactive elements require that the manufacturing process be accomplished remotely in a heavily-shielded location.
Based on operational requirements for a commercial nuclear plant, the fuel pellets should have a high density (e.g., greater than 85% smeared theoretical density) in order to provide satisfactory performance. The complex pelletizing and sintering equipment and industrial pellet manufacturing techniques that are known in the art for producing high density fuel are not suitable for use in a heavily shielded, remotely operated manufacturing cell.
Thus, there is a need in the art to design and develop systems and processes for sintering and pelletizing high density, e.g., greater than 85% smeared theoretical density, highly radioactive element-containing pellets in a heavily shielded, remotely operated area. Further, it is desired that the sintering and pelletizing processes can be carried out from a remote location, e.g., inside the heavily shielded area, using equipment which requires minimal maintenance throughout its lifetime and allows for straightforward process automation.